In malignant gliomas mutation and/or loss of function of p53 protein is a common event and is thought to play a role in resistance to ionizing radiation (IR) that contribute to the poor prognosis of these tumors. Ribonucleotide reductase (RNR) is a key enzyme for converting ribonucleotides into deoxyribonucleotides, an activity crucial for DNA replication. Inhibition of this enzyme correlates to an increase in radiosensitivity in several types of malignancies. Recently, a new gene inducible by p53 after DNA damage, called p53R2, was identified that codes for one subunit of this enzyme. Thus, we seek to investigate the role of this enzyme in the radiosensitivity and progression of malignant gliomas. Therefore, the long term goal of this proposal is to demonstrate that inhibition of ribonucleotide reductase, by using polyhydroxy-substituted benzohydroxamic acid derivatives, a new generation of synthetic drugs, or antisense oligonucleotides, is able to decrease tumor growth by interfering with the DNA repair ability of cells exposed to ionizing radiation. In vitro studies using Western blot analysis, RT-PCR and proliferation assays will be performed to determine: 1) the effect of RNR inhibitors on tumor cell proliferation, 2) the effect of combination of IR and RNR inhibitors on the expression of RNR subunits, in particular the p53R2, in glioma cells with different p53 status, and 3) the mechanism of action of these inhibitors in glioma cells. In vivo studies using the rat glioma model will be performed to evaluate the effect of RNR inhibitors and IR treatment on tumor progression and animal survival. Intraperitoneal injection and intratumoral infusion of the drugs, techniques well established in the laboratory, will be used.